Historian Niall Ferguson‘s latest Newsweek column offers several reasons why Americans can’t afford (no pun intended) to ignore the financial problems plaguing the Old World:

[T]he third reason Americans should care about Europe is more important even than the risk of a renewed financial crisis. It is the danger that what is happening in Europe today could ultimately happen here. Just a few months ago, almost nobody was worried about Italy’s vast debt, which amounts to 121 percent of GDP. Then suddenly panic set in, and Italy’s borrowing costs exploded from 3.5 percent to 7.5 percent.

Today the U.S. gross federal debt stands at around 100 percent of GDP. Four years ago it was 62 percent. By 2016 the International Monetary Fund forecasts it will be 115 percent. Economists who should know better insist that this is not a problem because, unlike Italy, the United States can print its own money at will. All that means is that the U.S. reserves the right to inflate or depreciate away its debt. If I were a foreign investor—and half the debt in public hands is held by foreigners—I would not find that terribly reassuring. At some point I might demand some compensation for that risk in the form of … higher rates.

Athens, Rome, Washington … The shortest route from imperial capital to tourist destination is precisely this death spiral of debt.